A tube pump is conventionally known that pumps liquid in a tube formed from an elastic member by intermittently compressing the tube with a plurality of rollers. Liquid output of the tube pump changes with the rotational speed of the rotor to which the rollers are attached.
The flow rate of the liquid being pumped intermittently by the tube pump may be controlled by measuring the flow rate of the liquid with a flow meter provided at a flow passage downstream of the tube pump and controlling the rotational speed of the rotor of the tube pump in accordance with the measured flow rate.
The flow meter, however, cannot measure the flow rate of the liquid correctly when the liquid being pumped intermittently by the tube pump is pulsating. Accordingly, the flow rate of the liquid being pumped by the tube pump cannot be controlled appropriately. The liquid is likely to pulsate greatly particularly when the rotor of the tube pump turns at a low speed and the liquid output of the tube pump is small.
As a device for suppressing the pulsations of the liquid being pumped by the pump, a damper is known that maintains the pressure balance between an air chamber and a liquid chamber provided therein to suppress the pulsations of the liquid being guided into the liquid chamber (see Japanese Unexamined Patent Application, Publication No. 2000-205201, for example).